Multi-combustor turbine

ABSTRACT

A system for the gradual oxidation of fuel is disclosed. The system includes an oxidizer that has a reaction chamber with an inlet and an outlet. The reaction chamber is configured to receive a fluid comprising an oxidizable fuel through the inlet. The oxidizer is configured to maintain a flameless oxidation process. The system also includes a heating chamber with an inlet and an outlet. The inlet of the heating chamber is in fluid communication with the outlet of the reaction chamber. The heating chamber is configured to receive the fluid from the reaction chamber and selectably heat the fluid.

BACKGROUND

1. Field

The present disclosure generally relates to systems and methods ofoperating a gas turbine and, particularly, operating a gas turbine froma low-energy content fuel.

2. Description of the Related Art

In a conventional gas turbine system, a high-energy-content fuel, forexample propane, is combusted as it is injected into pressurized air,thereby heating and increasing the thermal energy of the gas. The energyis then extracted from the heated gas with a turbine which convertsthermal energy into kinetic energy. The kinetic energy may be used todrive another device, for example an electric power generator. Thecombustion process is often initiated by an ignition source, for examplea spark plug. Due to the high energy content of the fuel, the combustionis very rapid and nearly instantaneous.

SUMMARY

One of the drawbacks of existing gas turbine systems is that theyrequire a high-energy-content fuel, such as propane (C₃H₈) that cansustain a continuous flame. It is desirable for a gas turbine to operateoff of low-energy-content fuel, such as the methane (CH₄) that evolvesfrom some landfills, with an exhaust that minimizes undesirablecomponents such as carbon monoxide (CO) and various nitrogen oxides.NO_(x) is a generic term for the mono-nitrogen oxides NO and NO₂ (nitricoxide and nitrogen dioxide). To accomplish this operation, the gasreaches a temperature that is high enough to convert all volatileorganic compounds (VOCs) in the incoming fuel/air mixture to carbondioxide (CO₂) and water (H₂O) and eliminate CO, while keeping themaximum gas temperature below the temperatures at which NO_(x) willform.

The disclosed turbine system uses a gradual oxidizer (also referred toherein as an oxidizer, a gradual oxidation chamber, an oxidationreaction chamber) in place of a combustion chamber to generate the heatthat drives the process. The oxidizer can contain material, such as aceramic, that is structured to be porous to a gas flow and retains itsstructure at temperatures above 1200 degrees Fahrenheit (F).

In some embodiments, the gradual oxidizer has a very large thermalinertia and is brought up to the operating temperature of 1000-1200° F.before the gradual oxidation process will occur. Therefore, the turbinesystem can be started under an alternate energy source, and when theoxidizer has been correctly heated, the system can transition from anoperation using the alternate energy source to an operation using thegradual oxidation process. In certain embodiments, a combustor is usedto start the turbine. Some embodiments provide that heat from theturbine exhaust warms incoming gas through a heat exchanger, but it maynot be sufficient to warm the oxidizer to a temperature that willsupport a gradual oxidation process. In certain embodiments, a warmer isused to heat incoming air at an inlet of the oxidizer in order to raisethe temperature of the oxidation chamber to a desired operationaltemperature range.

In certain embodiments a system for gradually oxidizing fuel isdisclosed. The system comprises an oxidizer having a reaction chamberwith an inlet and an outlet. The reaction chamber is configured toreceive a gas comprising an oxidizable fuel through the inlet. Theoxidizer is configured to maintain a flameless oxidation process. Thesystem also comprises a first heating chamber with an inlet and anoutlet. The inlet is in fluid communication with the outlet of thereaction chamber. The first heating chamber is configured to receive thegas from the reaction chamber and selectably heat the gas.

In some embodiments, the system further includes a turbine having aninlet and an outlet, the inlet of the turbine coupled to the outlet ofthe first heating chamber, the turbine configured to receive the gasfrom the first heating chamber. The system can further include, incertain embodiments, a compressor coupled to the inlet of the reactionchamber and further coupled to the turbine, the compressor configured tobe driven by the turbine to compress the gas prior to the gas beingreceived by the reaction chamber.

In some embodiments, the system includes a second heating chambercoupled between the compressor and the inlet of the reaction chamber,the second heating chamber being configured to receive the compressedgas from the compressor and to selectably heat the gas prior to the gasbeing received by the reaction chamber. Some embodiments provide thatthe system further includes a heat exchanger comprising a first portioncoupled between the compressor and the second heating chamber such thatthe gas from the compressor passes through the second portion before itis received by the second heating chamber and a second portion coupledto the outlet of the turbine such that the gas from the turbine passesthrough the second portion, the heat exchanger configured to thermallycouple the gas in the second portion to the gas in the first portion.

In some embodiments, the oxidizer includes a porous media disposedwithin the reaction chamber. The oxidizer can further include, incertain embodiments, at least one anchor heater that is at leastpartially disposed within the reaction chamber. Certain embodimentsprovide that the oxidizer does not comprise a catalyst for the oxidationprocess.

The oxidizer preferably is further configured to maintain the oxidationprocess when the fuel content of the gas is below a level that willsustain a continuous flame. In some embodiments, the oxidizer is furtherconfigured to maintain the oxidation process when the gas comprises lessthan 5% oxidizable fuel. In some embodiments, the oxidizer is furtherconfigured to maintain the oxidation process when the oxidizable fuel ismethane.

In certain embodiments, the first heating chamber includes a burnerconfigured to receive and ignite a combustible fuel-air mixture. Someembodiments provide that the second heating chamber comprises a burnerconfigured to selectably accept and ignite a combustible fuel-airmixture. In some embodiments, the system further includes a powergenerator coupled to the turbine, the power generator configured to bedriven by the turbine. Some embodiments provide that the gas comprisesat least one volatile organic compound (VOC); and the oxidizer achievesat least partial oxidation of the VOC.

In certain embodiments, a gradual oxidation system is disclosed. Thesystem comprises a compressor configured to receive and compress a gascomprising a fuel-air mixture. The system also comprises a warmercoupled to the compressor. The warmer is configured to receive the gasfrom the compressor and to selectably heat the gas. The system alsocomprises a reaction chamber coupled to the warmer. The reaction chamberis configured to receive the gas from the warmer and maintain aflameless oxidation process of the fuel-air mixture without a catalyst.The system also comprises a heater coupled to the reaction chamber. Theheater is configured to receive the gas from the reaction chamber andselectably heat the gas. The system also comprises a turbine coupled tothe heater and further coupled to the compressor. The turbine isconfigured to receive the gas from the heater and expand the gas todrive the compressor.

In some embodiments, the system includes a controller coupled to thewarmer and the heater, the controller configured to control the heatingof the gas in the warmer and in the heater. In some embodiments, thecontroller is coupled to a first sensor that measures a firsttemperature of the gas at the outlet of the reaction chamber, thecontroller further configured to cause the warmer to heat the gas untilthe first temperature reaches a first setpoint.

Some embodiments provide that the controller is coupled to a secondsensor that measures a second temperature of the gas at the inlet of theturbine, the controller is further configured to cause an adjustment inthe fuel provided to the oxidizer until the second temperature reaches asecond setpoint. In some embodiments, the system further includes apower generator coupled to the turbine and the controller, wherein theturbine is further configured to drive the power generator and thecontroller is further configured to control the power generator tomaintain the turbine speed within a range.

In certain embodiments, a method of gradual oxidation is disclosed. Themethod includes the steps of compressing a gas comprising a mixture ofair and an oxidizable fuel, heating the compressed gas to a firsttemperature that exceeds an auto-ignition temperature of the fuel, andmaintaining the gas above the first temperature for at least a firstperiod of time sufficient to accomplish at least a desired degree ofoxidation of the fuel, thereby forming an oxidized gas, e.g., a gascomprising the products of oxidation of at least a portion of theoxidizable fuel in the original gas/air mixture.

In some methods, the step of compressing the gas is accomplished using acompressor; and the method further comprises the steps of (i) expandingthe oxidized gas using a turbine; and (ii) driving the compressor withthe turbine. Some methods further include the step of heating theoxidized gas to at least a second temperature. In some methods, the stepof heating the compressed gas comprises passing the compressed gasthrough a first portion of a heat exchanger and the oxidized gas througha second portion of the heat exchanger such that heat is transferredfrom the oxidized gas to the compressed gas.

In some methods, the step of heating the compressed gas comprisespassing the compressed gas through a warmer configured to heat thecompressed gas. Some methods provide that the step of maintaining thegas above the first temperature comprises maintaining the gas below athird temperature.

The details of one or more embodiments of these concepts are set forthin the accompanying drawings and the description below. Other features,objects, and advantages of these concepts will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide furtherunderstanding and are incorporated in and constitute a part of thisspecification, illustrate disclosed embodiments and together with thedescription serve to explain the principles of the disclosedembodiments.

FIG. 1 is a schematic diagram of an example existing gas turbine system.

FIG. 2 is a schematic of a multi-combustor turbine system according tocertain aspects of this disclosure.

FIG. 3 is a schematic of a fuel supply system according to certainaspects of this disclosure.

FIG. 4A is a schematic of a start-up system according to certain aspectsof this disclosure.

FIG. 4B is a schematic of another embodiment of a start-up systemaccording to certain aspects of this disclosure.

FIG. 5 is a cross-section of an exemplary oxidizer according to certainaspects of this disclosure.

FIG. 6 is cross-section of an exemplary combustor according to certainaspects of this disclosure.

FIG. 7A is a perspective view of an exemplary burner according tocertain aspects of this disclosure.

FIG. 7B is a front view of the burner of FIG. 7A according to certainaspects of this disclosure.

FIG. 7C is a cross-section of the burner of FIG. 7A according to certainaspects of this disclosure.

FIG. 8 is a perspective view of an anchor heater according to certainaspects of this disclosure.

FIG. 9 is a perspective view of an exemplary porous element according tocertain aspects of this disclosure.

FIG. 10 is a flowchart of an exemplary start-up process according tocertain aspects of this disclosure.

FIG. 11 is a simplified schematic of the multi-combustor turbine systemof, for example, FIG. 2 according to certain aspects of this disclosure.

FIG. 12 is a control diagram of the control loop for the temperature ofthe gas at the oxidizer outlet according to certain aspects of thisdisclosure.

FIG. 13 is a control diagram of the control loop for the speed of thegenerator, turbine, and compressor according to certain aspects of thisdisclosure.

FIG. 14 is an exemplary schematic of a power generation system accordingto certain aspects of this disclosure.

FIG. 15 depicts a more detailed description of the control process ofFIG. 10 with respect to, for example, the system of FIG. 14 according tocertain aspects of this disclosure.

FIG. 16 depicts an exemplary turbine speed control loop adapted for theprocess of, for example, FIG. 15 according to certain aspects of thisdisclosure.

FIG. 17 depicts an exemplary power output control loop adapted for theprocess of, for example, FIG. 15 according to certain aspects of thisdisclosure.

FIG. 18 is an exemplary schematic of a power generation system accordingto certain aspects of this disclosure.

FIG. 19 depicts a more detailed description of the control process ofFIG. 10 with respect to, for example, the system of FIG. 18 according tocertain aspects of this disclosure.

FIG. 20 depicts an exemplary speed and temperature control loop adaptedfor the process of, for example, FIG. 19 according to certain aspects ofthis disclosure.

FIG. 21 is a plot of experimental data illustrating an exemplarystart-up process of a multi-combustor turbine system according tocertain aspects of this disclosure.

DETAILED DESCRIPTION

The following description discloses embodiments of a system foroxidation of a fluid that comprises an oxidizable fuel. In certainembodiments, the system includes a turbine combustor that can be used tostart up the system and a warmer combustor that can be used to warm upan oxidizer, or oxidation chamber, to a temperature at or near theauto-ignition temperature of the fuel in the fluid. The system isparticularly adapted for utilization of a fluid with a low energycontent, such as a methane content below 5%, in a sustainable gradualoxidation process to drive a turbine that further drives a powergenerator as well as driving a compressor in the system. In certainembodiments, the system also reduces undesirable components, such as COand NO_(x), in the exhaust that is vented to the atmosphere.

In the following detailed description, numerous specific details are setforth to provide an understanding of the present disclosure. It will beapparent, however, to one ordinarily skilled in the art that embodimentsof the present disclosure may be practiced without some of the specificdetails. In other instances, well-known structures and techniques havenot been shown in detail so as not to obscure the disclosure.

The method and system disclosed herein are presented in terms of aturbine system that drives a power generator using a methane-containinggas as a fuel gas and a commercially pure gas, such as methane orpropane, as an auxiliary gas. Nothing in this disclosure should beinterpreted, unless specifically stated as such, to limit theapplication of any method or system disclosed herein to a particularfuel gas or auxiliary gas or a turbine system of this particularconfiguration. Other configurations of turbine-compressor systems areknown to those of skill in the art and the application of the componentsand principles disclosed herein to other systems will be apparent.

FIG. 1 is a schematic diagram of an example gas turbine system 10. Inthis system, air at state 1, discussed in greater detail below, is drawninto compressor 14 through the inlet line 12. The compressor 14 raisesthe pressure and temperature of the air to state 2 in line 16. As thegas leaving the turbine 22 is hotter than the gas leaving the compressor14, it is possible to heat up the air before it enters the combustionchamber 18 using a heat exchanger 30. This results in lower fuelconsumption in the combustion chamber 18 to produce the same temperatureof the gas at the turbine inlet line 20 and makes the system 10 moreefficient.

The compressed air flows through the incoming side 32 of the heatexchanger 30 which raises the temperature of the gas to state 3 in line36. The compressed air enters the combustion chamber 18 where ahigh-energy content fuel 40, such as propane or natural gas, is injectedand ignited within the combustion chamber 18, thereby raising the gastemperature to state 4 coming out of the combustion chamber 18 in line20.

The hot compressed gas enters the turbine 22 which converts a portion ofthe energy in the gas into rotational kinetic energy in the turbine. Inthe embodiment of FIG. 1, this rotational kinetic energy is used to turna generator 24 that generated electric power and the compressor 14 thatare mounted on a common shaft 26 with the turbine 22.

The gas exits the turbine at a pressure and temperature of state 5 andflows through line 28 to the outgoing side 34 of the heat exchanger 30.In the heat exchanger 30, heat from the relatively hot exhaust gas istransferred to the relatively cold inlet air, as previously mentioned.The cooled exhaust gas exits the heat exchanger at state 6 through line38 and is vented to the atmosphere.

The compression of the air from state 1 to state 2 in the compressor canbe considered, in an idealized model, as an isentropic compressionrequiring power input. The changes from state 2 to 3 and from state 3 to4 are constant-pressure increases in temperature that require heat inputprovided through the heat exchanger 30 and combustor 18, respectively.The expansion of the gas from state 4 to 5 in the turbine is anisentropic expansion that produces a power output. Cooling of theexhaust gas from state 5 to 6 is a constant pressure process with heatremoval in the heat exchanger 30, which is accomplished by transferringheat from the hot exhaust gas in outgoing side 34 of the heat exchanger30 to the relatively cold inlet gas in the incoming side 32.

FIG. 2 is a schematic of a multi-combustor turbine system 50 accordingto certain aspects of this disclosure. In this embodiment, an oxidizer60 replaces the combustion chamber 18 of FIG. 1 to generate the heatthat drives the process. A combustor 64 is located between the oxidizer60 and the turbine 66 to provide a secondary method of heating the gasbefore the gas enters the turbine 66. In certain embodiments, thiscombustor 64 is used to heat the gas during start-up of the turbinesystem 50.

In certain embodiments, it is desirable to heat the gas entering theoxidizer 60 during start-up so as to facilitate raising the temperatureof the oxidizer 60 to an operational temperature. In the embodiments ofFIG. 2, this can be accomplished by the warmer combustor 62 locatedbetween the compressor 14 and oxidizer 60. In certain embodiments, thisis accomplished by an electric heater (not shown), and in certainembodiments, a gas-operated heater or combustor can facilitate raisingthe temperature of the gas that is introduced into the oxidizer 60. Inthe embodiments of FIG. 2, a heat exchanger 30 is used to heat the gascoming out of compressor 14 before the gas enters the warmer combustor62 or the oxidizer 60.

In turbine system 50, air is drawn into compressor 14 through line 12with the addition that a fuel gas 52 is added to the incoming airthrough line 56 and valve 54. The fuel-air mixture is carried throughline 58 into the compressor 14. In certain embodiments, this fuel gas 52is a low-energy-content methane-containing gas that is delivered from anexternal source such as a landfill. The composition of this fuel gas 52is highly dependent upon the specific site and source.

As a first example of a low-energy-content fuel, gas emanating from alandfill contains only 2 percent methane. In another exampleapplication, the fuel gas contains approximately 50% methane and 45%CO₂, with the balance of the gas comprising organic compounds andhydrogen sulfide. In certain embodiments, the fuel gas 52 is blendedwith air to produce a fuel-air mixture having a methane concentrationwithin a target range for the turbine system 50. In certain embodiments,the fuel gas 52 is fed undiluted into compressor 14. The compressor 14compresses this fuel-air mixture to state 2 in line 16.

The fuel gas 52 may include a single type of fuel and/or multipledifferent types of fuel, one or all of which may be oxidized in theoxidizer. The fuel gas 52 may include hydrocarbon fuel and/or othertypes of fuel. The fuel gas 52 may be weak fuel. Weak fuels may includelow BTU gases (i.e., low energy per unit mass) and/or fuels having lowcalorific value. Weak fuels may include gases containing fuels below aconcentration that can sustain an open flame and/or other combustionreaction. For example, fuel may be mixed with air with the resultantfuel concentration below a lower explosive limit (LEL) for the fuel.

In some instances, introducing such a weak fuel to a spark or flame,even in the presence of air, may snuff out the spark or flame withoutoxidizing the fuel in the mixture. However, when the weak fuel is raisedto a temperature above its auto-ignition temperature, the fuel canoxidize in the presence of air without introduction of a spark or flame.A specific example of weak fuels include gas that is mostly carbondioxide or nitrogen, containing small quantities of methane, ethane,carbon monoxide, and other types of fuel. Such gas is often emitted fromso-called unproductive natural gas wells. The fuel gas 52 may includefuels other than, or in addition to, weak fuels. For example, in someimplementations, the fuel gas 52 may include propane, butane, kerosene,gasoline, and/or other types of fuels in addition to, or instead of,weak fuels. In some cases, the fuel gas 52 may be hydrogen fuel.

The fuel gas 52 may include gas emanated from a landfill, which maycontain only a small percentage of methane fuel (e.g., about 3-5 percentor less). A gas having such a low concentration of methane may be belowa lower explosive limit. The lower explosive limit (LEL) of a fuel mayrefer to the lowest concentration of the fuel in air capable ofproducing a flash of fire in presence of an ignition source.Concentrations lower than the LEL are typically too weak for combustion.Different types of fuel have different LEL values, typically in therange of approximately about 1 percent to about 5 percent by volume,although some fuels have an LEL outside of this approximate range. Someparticular examples of LEL values are (approximately, on a volumetricbasis) 3 percent for ethane, 4 percent for hydrogen, 5 percent formethane, and 2 percent for propane.

Fuel in the fuel gas 52 can be a natural (e.g., non-anthropological)fuel source or a human-made (e.g., anthropological) fuel source. Forexample, the fuel gas 52 may include methane from cattle belches, aswampland, a rice farm, and/or methane produced by fermentation or otherbiological or chemical processing of organic matter. Other example fuelsources can include manure, municipal waste, wetlands, gas seeping fromleaks in the system or other systems, and drilling and recoveryoperations. In some implementations, the fuel gas 52 includes fuel mixedwith water. One or more supplemental fuels may also be utilized by theoxidizer. For example, gas fuels can be provided to the system, andliquid fuels can also be provided to the system.

In some embodiments, combustion gases can be added to the system toadjust performance or operation of the system. For example, inembodiments where a low fuel content mixture does not contain enoughfuel for self-sustainable destruction, or in which the oxidation processis incapable of being maintained based on fuel content in the fuel gas52 alone, combustion gases can be added with air prior to or after thecompressor to provide sufficient fuel for the self-sustaining oxidationprocess. Combustion gases that can be added include, for example withoutlimitation, hydrogen, methane, ethane, ethylene, natural gas, propane,propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene,iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide.

The amount of combustion gases added can be adjusted based on the amountof fuel detected in the fuel gas 52. If there is an undesirableconcentration of fuel in the fuel gas 52, the amount of combustion gasesadded can be increased or decreased in response. In some embodiments,the amount of combustion gases added is based on the amount of fuelcontent in the fuel gas 52 received by a fuel gas source. In someembodiments, the amount of combustion gases added prior to introducingthe fuel gas 52 to the system is based on a temperature of the oxidizer.In some embodiments, the amount of combustion gases added is based on acombination of the amount of fuel content in the fuel gas 52 and adesired change in the temperature or the rate of change of temperaturewithin the oxidizer 60.

With reference to FIG. 2, the fuel-air mixture passes through theincoming side 32 of the heat exchanger 30 and raises the temperature ofthe fuel-air mixture to state 3 in line 78. In the embodiment of FIG. 2,the fuel-air mixture then enters the warmer combustor 62 where anauxiliary fuel 54, for example propane, can be added to heat thefuel-air mixture. The combustion in or from the warmer combustor 62thereby further raises the temperature of the gas to state 7 in line 68.

The gas then enters the oxidizer 60, where the fuel undergoes a gradualoxidation process. The fuel may transfer a portion of its thermal energyinto the structure of the oxidizer 60, thereby raising the temperatureof the oxidizer 60. Optionally, additional auxiliary fuel 54 is injectedinto the gas and ignited in the turbine combustor 64, further raisingthe temperature of the gas leaving the turbine combustor 64 in line 72to state 4 that is sufficient to run the turbine 66. Turbine 66 can besimilar to the turbine 22 of FIG. 1 but, in certain embodiments, can beconfigured to work with a different pressure and temperature of gas.Turbine 66 extracts kinetic energy from the heated gas and drives thecompressor 14 and, in certain embodiments, the generator 24 and exhauststhe gas at state 5 in line 74.

In steady-state operation, the warmer combustor 62 and turbine combustor64 are turned down or off, such that little or no auxiliary fuel 54 isbeing injected into the gas within these combustors. The compressedfuel-air mixture coming out of the compressor 14 is heated in the heatexchanger 30 to a temperature that is below the oxidation temperature ofthe fuel in the gas. In this operational mode, state 7 of the gas issubstantially the same as state 3. After the gas enters the oxidizer 60,the gas is heated by contact with the structure of the oxidizer 60 or bythe temperature of heated gas within the oxidizer 60 to a temperaturesufficient to cause gradual oxidation of the fuel and organic compoundsin the gas, thereby generating heat. This process maintains thetemperature of the oxidizer 60 while also raising the temperature of thegas leaving the oxidizer at state 8 to a temperature sufficient tooperate the turbine 66.

Start-up of the turbine system 50 using one or both of the warmercombustor 62 and the turbine combustor 64 may include additionalequipment described in FIGS. 3 and 4. The start-up process is discussedin greater detail with respect to FIG. 10.

The composition of the gas that is passing through the various elementsof system 50 varies along the flow path. For example, the fuel gas 52may include entrained liquid that adheres to surfaces of system elementsand is thereby removed from the fluid. As a second example, an auxiliaryfuel 54 with or without additional air may be injected into the fluidflow before or at the warmer combustor 62 or the turbine combustor 64.This auxiliary fuel can be ignited, thereby adding combustion productsand other fluids to the fluid flowing through the system. The term“fluid” is used herein to refer to the mixture of gases, liquids, fuels,and other materials that are flowing through the system 50 regardless ofthe composition of the mixture.

The composition of the gas entering the oxidizer 60 depends heavily onthe source of the fuel gas 52. For a facility such as a landfill,methane-containing gas is generated within the landfill. This gas can becaptured using a system of vent tubes placed in the landfill. The gasemanating from the landfill will contain a variable amount of methane aswell as numerous other VOCs as well as entrained liquid and particles.The amount of fuel gas 52 injected into the air line 12 at the inlet ofthe compressor 14 depends on the methane content of the fuel gas, withthe intent of achieving a consistent methane content of the gas thatenters the compressor 14. In certain embodiments, the gas (e.g.,methane) content is desired to be less than about 5% of the total volumeof gas. In certain embodiments, the gas (e.g., methane) content isdesired to be less than about 2% of the total volume of gas.

One of the benefits of the turbine system 50 is that the gas that isvented to the atmosphere from line 76 contains a very low amount ofundesirable gases such as methane, CO, and NO_(x). For a facility suchas a landfill, the methane-containing gas emanating from the landfill isconsidered a pollutant. In certain embodiments, the turbine system 50uses the methane-containing gas emanating from the landfill as fuel-gas52 and converts nearly all of the methane and other VOCs to CO₂ and H₂O.In certain embodiments, the system 50 can reduce formation of NO_(x) bymaintaining a maximum temperature of the fluid below 1300° C. Thus, theturbine system 50 cleans up a potential source of pollution compared todirect venting of the methane-containing gas emanating from the landfillor use of a flare facility that burns the methane-containing gas atcombustion temperatures that may exceed 1300° C. and thereby allow theformation of CO and NO_(x).

FIG. 3 is a schematic of a gas supply system 80 according to someembodiments of this disclosure. A fuel gas, such as a methane-containinggas emanating from a landfill, is received through line 86. In certainembodiments, this gas is at a pressure above ambient atmosphericpressure. In certain embodiments, this gas is at atmospheric pressure.In certain embodiments, this gas is being actively collected and is at apressure below ambient. The incoming gas may have liquid entrained inthe gas as it enters the line 86.

The gas may pass through a vapor-liquid separator that is often called a“knockout drum.” Within knockout drum 82, the entrained liquid tends toseparate and fall to the bottom of the knockout drum 82, from which theliquid is at least periodically drained off, while the gas having areduced amount of entrained liquid passes out at the top of the knockoutdrum 82. Devices of this type are known to those of ordinary skill inthe art. The gas from the knock drum 82 enters the inlet of blower 84,which pressurizes the gas to slightly above atmospheric pressure, suchas 1.1 pounds per square inch above ambient, i.e. gauge pressure (psig),in outlet line 88. Line 88 of FIG. 3 is equivalent to line 56 of FIG. 2,wherein the pressurized gas is mixed with ambient air at the inlet ofthe compressor 14. In certain embodiments, the pressurized gas providedby the gas supply system 80 is of sufficient quantity and containssufficient oxygen to supply the compressor 14 without requiringadditional ambient air.

FIG. 4A is a schematic of a start-up system 90A according to certainaspects of this disclosure. The start-up system 90A comprises a supplyof an auxiliary fuel 54, with reference to FIG. 2. In the embodiment ofFIG. 4, this auxiliary fuel supply 54 comprises at least onecompressed-gas cylinder 94 of a high-energy fuel such as propane ormethane. In the embodiment of FIG. 4A, the fuel from cylinders 94 is fedthrough a pressure regulator 96 into line 98 which conveys thepressurized gas to one or both of the turbine combustor 64 and thewarmer combustor 62. The use of this system 90A is discussed in greaterdetail with respect to FIG. 10.

FIG. 4B is a schematic of another embodiment of a start-up system 90Baccording to certain aspects of this disclosure. In this embodiment, thefuel gas that is received through line 86 of FIG. 3 contains sufficientcombustible undiluted fuel gas to sustain combustion. This fuel gas iscompressed in the start-up compressor 92 to a pressure that is above thepressure of the gas in lines 78 and 70 of FIG. 2, thereby allowing thegas to be injected into at least one of the warmer combustor 62 and theturbine combustor 64. The pressurized gas is provided on line 98. Incertain embodiments, the start-up system 90B includes an accumulator(not shown) attached to line 86. In certain embodiments, the start-upsystem 90B includes a reservoir (not shown) attached to line 98. Incertain embodiments, the start-up system 90B includes a recirculationline (not shown) that allows the start-up compressor 92 to run while notdelivering gas through line 98.

FIG. 5 is a schematic cross-section of an exemplary oxidizer 60according to certain aspects of this disclosure. The oxidizer 60includes a pressure vessel 122 having a reaction chamber 120. Gas isreceived through inlet 130 and, in this embodiment, flows through thedistribution tower 132 and then through the plurality of side tubes 134and into the reaction chamber 120. In this embodiment, the side tubesare perforated (not visible in FIG. 5) such that the gas exits the sidetubes 134 at a plurality of points along the side tubes 134. In certainembodiments, the side tubes are omitted and the gas exits directly fromthe tower 132 through perforations (not shown). In certain embodiments,the gas is dispersed within the oxidizer through a perforated container(not shown) located at the end of tower 132. In certain embodiments, theinterior cavity is at least partially filled with a porous media, suchas the ceramic “dog bones” shown in FIG. 9. The gas that exists the sidetubes 134 flows through the reaction chamber 120 and out through theoutlet 140.

The oxidizer 60 gradually oxidizes fuel by heating the fuel-air mixturereceived at inlet 130 to or above the fuel's auto-ignition temperatureto initiate a spontaneous oxidation reaction. The temperature of thereaction chamber 120, and any media contained in the reaction chamber120, is maintained within a temperature range selected to maintaingradual oxidation. The fuel concentration and flow rate may beadditionally or alternatively controlled to maintain gradual oxidation.

By gradually oxidizing fuel, the oxidizer 60 can enable enhanced controlover the fuel oxidation process, thereby accomplishing complete orsubstantially complete oxidation of the fuel constituents and thusreducing the emission of un-oxidized fuels into the environment. Thegradual oxidation process may also reduce thermally generatedenvironmental pollutants (e.g. NO_(x)) and reduce or eliminate the needfor expensive catalyst materials. In certain embodiments, the formationof NO_(x) can be reduced by maintaining the maximum temperature of allpoints along the flow path below a temperature such as 1300° Celsius(C). In certain embodiments, the oxidizer 60 may reduce or eliminate theformation of contaminants (e.g. silica) that can form during thecombustion of certain fuel gases and are harmful to gas turbine systemcomponents. In certain embodiments, the oxidizer 60 may also trap thecontaminants (e.g. silica) and prevent the contaminants from reachingthe turbine 66.

The volume and shape of the reaction chamber 120 can be designed toprovide a low flow rate through the reaction chamber 120, allowingsufficient time for the fuel oxidation reactions to be completed. As anexample, if the reaction chamber 120 is designed such that the averageflow rate is less than ten feet per second and the length of the chamberis ten feet, then the average residence time of the gas in the chambercan be at least one second.

The volume and shape of the reaction chamber 120, and the configurationof the overall system, can be designed to provide a controlled flow andflow rate through the chamber, allowing sufficient residence time forcomplete fuel oxidation. The flow path can be sufficiently long that aflow rate of the air and fuel mixture along the flow path, averaged overthe length of the flow path, allows the fuel to oxidize to completion.As an example, the average residence time of the gas in the chamber canbe equal to or greater than one second in some cases. The averageresidence time of the gas in the chamber can be less than one second insome cases.

In some embodiments, the residence time of the gas in the chamber canrange from about 0.1 second to about 10 seconds. In some embodiments,the residence time of the gas in the chamber can range from about 0.5second to about 5 seconds. In some embodiments, the residence time ofthe gas in the chamber can range from about 0.5 second to about 2seconds. In some embodiments, the residence time of the gas in thechamber can range from about 0.5 second to about 1 second. In someembodiments, the residence time of the gas in the chamber can range fromabout 1 second to about 2 seconds. In some embodiments, the residencetime of the gas in the chamber can be less than about 0.1 second or morethan about 10 seconds. The rate of oxidation of the mixture is afunction of the constituents of the fuel, fuel concentration, oxygenconcentration, pressure, temperature and other factors. Thus, the rateof oxidation can be adjusted by adjusting these parameters accordingly.

The thermal mass of the material within the reaction chamber 120 mayhelp stabilize temperatures for gradual oxidation of the fuel. Incertain embodiments (e.g. when there is an oversupply of fuel in thereaction chamber 120), the thermal mass within the reaction chamber 120may act as a dampener, absorbing some heat and protecting the turbinefrom excessively hot gas leaving the oxidizer 60. In other cases (e.g.when there is a low supply of fuel in the reaction chamber 120), thethermal mass within the reaction chamber 120 may provide a temporarysource of energy, helping to sustain oxidation of the fuel. In certainembodiments, the oxidizer 60 includes a flame arrestor (not shown) nearthe inlet 130 that is configured to suppress transfer of heat energy outof the reaction chamber 120, thereby confining the oxidation reaction tothe reaction chamber 120.

The reaction chamber 120 may also be adapted to promote mixing of thefuel-air mixture as it flows through the reaction chamber 120. Forexample, the reaction chamber 120 may include flow diverters to controla residence time (e.g. an amount of time a given volume of the fuel-airmixture traverses the flow path through the reaction chamber 120) and/orto help maintain the temperature in certain regions within the reactionchamber 120 at or near a specified temperature, e.g. the auto-ignitiontemperature of the fuel. As another example, the reaction chamber 120may include internal heat transfer zones, where a hotter section of theflow path imparts heat to a cooler section of the flow path within thereaction chamber 120.

In certain embodiments, one or more heat sources are disposed within thereaction chamber 120 to achieve the appropriate temperature distributionwithin the reaction chamber 120. In certain embodiments, these heatsources are anchor heaters 124 shown in FIG. 5 and discussed in greaterdetail in FIG. 8.

FIG. 6 is a cross-section of an exemplary combustor 63 according tocertain aspects of this disclosure. In this embodiment, the combustor 63includes a housing 152 having a combustion chamber 150 through which gasflows from the inlet 154 to the outlet 156 as indicated by the arrow. Inthis embodiment, a burner 100 is located at an upstream end of thecombustion chamber 150. The burner is discussed in greater detail withrespect to FIGS. 7A-7C. In certain embodiments, the combustor 63comprises an electric heater (not shown). In certain embodiments, thecombustor 63 comprises an external burner (not shown) that heats the airflowing through the combustion chamber 150 without using the gas withinthe combustion chamber 150 as part of the combustion process of theexternal burner.

FIG. 7A is a perspective view of an exemplary burner 100 according tocertain aspects of this disclosure. In this embodiment, the burner 100is circular. A gas comprising a flammable fuel is fed into thedistribution channel 102 and dispersed through a plurality of orifices108 into a combustion channel 106 that surrounds the fluid channel 110.When installed in a combustor 63 as illustrated in FIG. 6, the fluidpassing from the inlet 154 through the combustion chamber 150 to theoutlet 156 passes at least partially through the fluid channel 110 whilethe combustion reaction is taking place in the surrounding combustionchannel 106. Combustion products from the combustion reaction arecarried away by the fluid flowing through the combustor 63.

In certain embodiments, the gas fed into the distribution channel 102comprises oxygen to at least partially support the combustion reaction.In certain embodiments, the gas fed into the distribution channelcomprises sufficient oxygen to fully support the combustion reaction,such that the fuel-air mixture of the fluid coming in through the inlet154 is appropriate for the oxidation process that takes place in theoxidizer 60 regardless of whether the burner 100 is operating.

FIG. 7B is a front view of the burner 100 of FIG. 7A according tocertain aspects of this disclosure. The fluid channel 110 has a cleardiameter 112 and the combustion channel 106 is formed from shapedelements 104A and 104B such that the gas orifices 108 are positioned, inthis embodiment, at a radial midpoint in the combustion channel 106.

FIG. 7C is a cross-section of the burner 100 of FIG. 7A according tocertain aspects of this disclosure. The cross-section is taken alongdashed line C-C in FIG. 7B and is shown without the background toenhance clarity. The distribution channel 102 has a nominal diameter114. The profiles of shaped elements 104A and 104B can be seen in theview of FIG. 7C.

FIG. 8 is a perspective view of an anchor heater 124 according tocertain aspects of this disclosure. The base 160, in this embodiment,penetrates the pressure vessel 122 such that the heating elements 162are located within the reaction chamber 120. In certain embodiments, theheating elements 162 have active portions 166 that generate heat andinactive portions 164 that are conductive but do not generate asignificant amount of heat.

FIG. 9 is a perspective view of an exemplary porous element 170according to certain aspects of this disclosure. The element comprises ashaped structure 172 having, in this embodiment, two holes 174A and174B. The shaped structure 172 comprises a refractory material. Incertain embodiments, the heat-resistant material is a ceramic. Incertain embodiments, a plurality of porous elements 170 are disposed inthe reaction chamber 120 of the oxidizer 60. In certain embodiments, theporous elements 170 are piled randomly within the reaction chamber 120such that at least one tortuous flow path exists from the inlet 130 tothe outlet 140 through the plurality of porous elements 170. In certainembodiments, the porous elements have other shapes. In certainembodiments, the reaction chamber 120 contains a structured ceramicpacking (not shown).

FIG. 10 is a flowchart of an exemplary start-up process 200 according tocertain aspects of this disclosure. The process shown in FIG. 10 isrelated to the system 50 of FIG. 2. The starting configuration of thisprocess is that the linked turbine 22, compressor 14, and generator 24are stopped, the fuels 52 and 54 are not being supplied, and theelements of system 50 are at ambient temperature, sometimes referred toas “cold.” In order to simplify the description herein it will berecognized that the turbine 22, compressor 14, and generator 24 arefixedly attached to a common shaft 26, and it will be understood that areference to a speed of any one of the turbine 22, compressor 14, orgenerator 24 implies that the other elements are rotating at the samespeed.

In step 205, the turbine 22 is started and brought up to a first speedS1 using an auxiliary drive. In certain embodiments, the generator 24can be driven as a motor, powered from an external power source, and actas the auxiliary drive. In certain embodiments, a separate motor (notshown in FIG. 2) is provided to start up the turbine. In certainembodiments, this separate motor is an electric motor. In certainembodiments, this separate motor is a gasoline or diesel engine. Forexample, speed S1 may be 16,000 revolutions per minute (RPM).

In step 210, the turbine 22 is held at speed S1 for an amount of time P1while air is drawn in through line 12 into compressor 14 without theaddition of fuel gas 52 or auxiliary gas 54. Compressor 14 compressesthe air and pushed the compressed air through the system 50 to theturbine 22 so as to purge the system. In certain embodiments, theturbine 22 may be held at a speed different from S1 or allowed to varyover the time P1. In certain embodiments, the speed of the turbine 22 isallowed to drop to a lower speed (not shown in FIG. 10) such as, forexample, 10,000 RPM after time P1 has elapsed.

Auxiliary fuel 54 is supplied to turbine combustor 64, and the turbinecombustor 64 is ignited in step 215. In certain embodiments, auxiliaryfuel 54 is a commercially available fuel gas, such as propane, providedby a start-up system 90A as shown in FIG. 4A. In certain embodiments,auxiliary fuel gas 54 is provided by a start-up system 90B such as shownin FIG. 4B, wherein the fuel gas 52 is compressed by compressor 92. Oncethe turbine combustor 64 is lit, the auxiliary drive is shut off in step220 and the turbine 22 is driven by the hot, compressed gas provided bythe turbine combustor 64. The turbine 22 is brought up to a speed S2using the turbine combustor 64. For example, speed S2 may be 52,000 RPM.During this time, the amount of fuel provided by start-up systems 90A or90B may be controlled by a first controller (not shown in FIG. 2) thatsenses the speed of the turbine 22 and the temperature of the gas at theinlet of the turbine 22.

When the turbine 22 reaches speed S2 in step 225, the power generator 24is activated. The generation of electric power by the power generator 24places a load on the turbine 22. In certain embodiments, a secondcontroller (not shown in FIG. 2) senses the speed of the turbine 22 andcontrols the amount of power being generated by the power generator 24,thereby varying the load on the turbine 22. While the first controlleris maintaining the temperature of the gas at the inlet of the turbine 22at a setpoint S1, the second controller maintains the speed of theturbine 22 at speed S2 by varying the load.

Maintaining the turbine 22 at a constant speed S2 stabilizes the flowrate of fluid through the system 50. In the embodiments of system 50shown in FIG. 2, the hot, expanded exhaust gas from turbine 22 isdirected through the “hot” portion 34 of heat exchanger 30 as the coolergas leaving the compressor 14 is directed through the “cold” portion 32of the heat exchanger 30. The heat exchanger 30 is configured tothermally couple the gas within the hot portion 34 to the gas within thecold portion 32. Heat will therefore be transferred from the hot gasleaving the turbine 22 to the cooler gas leaving the compressor 14. Thewarmed gas leaving the cold portion 32 of the heat exchanger 30 willheat the oxidizer 60. In certain embodiments, however, this heat is notsufficient to bring the temperature of the oxidizer 60 up to theauto-ignition temperature of the fuel gas 52. Additional heat can beadded to the oxidizer 60 to raise its temperature to the auto-ignitiontemperature of fuel gas 52.

In step 230, auxiliary gas 54 is provided to the warmer combustor 62 andthe warmer combustor 62 ignited. In certain embodiments, additional airis injected with the auxiliary fuel 54 to at least partially support thecombustion of the auxiliary fuel 54. Combustion of the auxiliary fuel 54creates heat within the warmer combustor 62 that further heats thecompressed gas that passed through the heat exchanger 30. In certainembodiments, the amount of fuel provided to the warmer combustor 62 maybe controlled by a third controller (not shown in FIG. 2) that sensesthe temperature of the gas at the outlet of the oxidizer 60. The heatprovided by the warmer combustor 62 will increase the temperature of theoxidizer 60 until it reaches a temperature setpoint T2 that is above theauto-ignition temperature of the fuel gas 52. For example, temperatureT2 may be 700° C. The temperature of the gas leaving the oxidizer 60will reflect the temperature of the oxidizer 60, as no fuel gas 52 isbeing provided yet and therefore there is no gradual oxidation processtaking place in the oxidizer 60.

When the temperature of the gas at the outlet 140 of the oxidizer 60reaches temperature T2 in step 235, valve 54 is opened and fuel gas 52is provided at the inlet of compressor 14. The fuel gas 52 will oxidizein oxidizer 60 thereby raising the temperature of the oxidizer 60 andthe temperature of the gas at the outlet 140. The third controllercontinues to regulate the warmer combustor 62 with a new setpoint of gastemperature T1 at the outlet of the oxidizer 60. For example, T1 may beabout 700° C. In certain embodiments, T1 may be about 900° C. In someembodiments, T1 may range from about 700° C. to about 900° C. In certainembodiments, T1 may be less than about 700° C. or greater than about900° C.

In step 240, when the temperature of the gas at outlet 140 reachestemperature T1, i.e., is sufficient to drive turbine 22 withoutadditional heat being provided by turbine combustor 64, the turbinecombustor 64 can be gradually or immediately shut off. When the thirdcontroller has reduced the operation of warmer combustor 62 to adetermined level, indicating that sufficient heat is being generated bythe oxidation process in oxidizer 60 to maintain the gas temperature atthe outlet 140 at temperature T1, the warmer combustor 62 is graduallyor immediately shut off.

Step 245 is the steady-state operation of the system 50. The thirdcontroller now regulates the amount of fuel gas 52 provided to the inletof compressor 14 so as to maintain temperature of the gas at the outletof the oxidizer 60, and therefore the temperature of the gas at theinlet of turbine 22, at temperature T1. The thermal mass of the oxidizer60, in certain embodiments, is sufficient to make the system 50 veryslow to respond to a change in the rate of delivery of fuel gas 52 atthe inlet to the compressor 14. In certain embodiments, the secondcontroller maintains the speed of the turbine 22 at speed S2 insteady-state operation by varying amount of power being generated by thepower generator 24 as previously discussed.

While the discussion of speed and temperature controllers herein ispresented in terms of a single-value setpoint, it will be apparent tothose of skill in the art that the setpoint may be a range of valuesassociated with the setpoint. For example, maintaining the speed ofturbine 22 at setpoint S2 should be interpreted to include maintainingthe speed of turbine 22 within a range between S2-low and S2-high.Similarly, reaching a temperature setpoint T1 should be interpreted toinclude the temperature teaching a lower limit T1-low of a range T1-lowto T1-high, and maintaining the temperature at setpoint T1 should beinterpreted to include maintaining the temperature between the upper andlower limits T1-low and T1-high.

In some embodiments, the system 50 is configured to reduce or eliminateformation of nitrogen oxides by maintaining a maximum temperature withinthe reaction chamber 120 that is below a threshold temperature ofconsiderable formation of nitrogen oxides. For example, in someembodiments, the maximum temperature within the reaction chamber 120 isbelow about 2300° F. In some embodiments, the maximum temperature withinthe reaction chamber 120 may range from about 1900° F. to about 2300° F.In some embodiments, the maximum temperature within the reaction chamber120 may range from about 2100° F. to about 2300° F. In some embodiments,the maximum temperature within the reaction chamber 120 may range fromabout 2200° F. to about 2300° F. In some embodiments, the maximumtemperature within the reaction chamber 120 can be greater than about2300° F. or less than about 1900° F.

FIG. 11 is a simplified schematic of the multi-combustor turbine systemof FIG. 2 according to certain aspects of this disclosure. Thisschematic depicts the elements that implement the control loops of FIGS.12 and 13 and is provided as a reference for those figures. Theschematic of FIG. 11 additionally shows power output 180 from powergenerator 24.

FIG. 12 is a control diagram of the control loop 300 for the temperatureof the gas at the oxidizer outlet 140 according to certain aspects ofthis disclosure. The gas temperature 183 is measured at the outlet 140of the oxidizer 60 and converted to a feedback signal 183A that iscombined with a temperature setpoint signal 182 at junction 196. Theresulting error signal 183B is fed into controller 190, which controlsthe fuel valve 54. The controller 190 adjusts the fuel valve 54 inresponse to the error signal 183B to change the fuel flow 56 into theinlet of compressor 14 and then into the oxidizer 60. The change in fuelflow 56 will change the amount of heat generated in oxidizer 60, therebychanging the gas temperature 183. As the oxidizer 60 may have a largethermal mass, this control loop 300 may have a very large time constant,resulting in a very slow response of the gas temperature 183 to changesin the error signal 183B.

FIG. 13 is a control diagram of the control loop 350 for the speed ofthe generator 24, turbine 22, and compressor 14 according to certainaspects of this disclosure. The turbine speed 186 is measured andconverted to a feedback signal 186A that is combined with a speedsetpoint signal 184 at junction 198. The resulting error signal 186B isfed into controller 192, which controls the power converter 194 (notshown separately) that is a part of the power generator 24. The powerconverter controls the amount of power being generated by the rotatingelements (not shown separately) of the power generator 24 and thereforecontrols the load 185 on the turbine 22 that is driving the rotatingelements. As the load 185 changes, and while the temperature of the gasat the inlet of the turbine 22 remains constant, the speed of theturbine 22 will change. Control system 350 has a small time constant,relative to the control loop 300, and so the turbine speed 186 canchanged much faster than the gas temperature 183.

Control loops 300 and 350 may be operated simultaneously as theircontrol bandwidths are separated. Control loop 300 can be considered theouter control loop, making very slow changes to the fuel flow 56 tocontrol the gas temperature 183, while control loop 350 can beconsidered the inner control loop making relatively fast changes to theload 185 to control the turbine speed. Due to the slow response ofcontrol loop 300, the gas temperature 183 will vary over long periods oftime while the fast, inner control loop 350 maintains the turbine speed186 constant as the varying gas temperature 183 appears to be constantrelative to the speed of response of control loop 350.

FIG. 14 is an exemplary schematic of a power generation system 400according to certain aspects of this disclosure. The system 400 includesa turbine system 410, a load module 420, and a power distribution module430. The turbine system 410 includes, in some embodiments, a wound rotorsynchronous generator (WRSG) 412 that provides three-phase power at 480volts of alternating current (VAC) at 60 Hz, a common configuration ofcommercial power grids. The WRSG 412 provides the three-phase power online 419A, shown in FIG. 14 as a single line although three-phase poweris transferred on at least three lines, to a power relay 413 capable ofswitching the entire current capacity of the system, for example 600 A.The function of power relay 413 is discussed in greater detail withrespect to FIG. 15. Line 419A also is connected to a circuit breaker414B that feeds the same three-phase power over line 419B to the loadmodule 420. When power relay 413 is closed, as shown in FIG. 14, thethree-phase power is provided to circuit breakers 414A and 414C. Circuitbreaker 414A is, in this embodiment, rated to the same capacity as thepower relay 413, for example 600 A, and then through output line 419C tothe power distribution panel 430. Circuit breaker 414C is rated to alower value, for example 50 A, and feeds power to an auxiliary loadpanel 416 to drive local loads 418 within the system. In certainembodiments, the auxiliary load panel 416 provides single phase 120 VACpower to the local loads 418.

The load module 420 includes one or more sets of relays 422 and loads424. In certain embodiments, the loads 424 are resistive elements. Themultiple loads 424 can be selectively connected to the output of theWRSG 412 to provide braking or to serve as a dummy load during start-upof the system 400 prior to closure of power relay 413. In certainembodiments, the total load of the load module 320, when all loads 424are connected, is 165 kW. In certain embodiments, the rating of circuitbreaker 414B is set to be below the peak current that can be handled bythe total load, for example 225 A for a 165 kW load module 420, wherein(225 A)(480 Vrms)(1.4)=152 kW.

The power distribution panel 430 is a standard commercial system whereinthe three-phase power coming in on line 419C is connected to adistribution bus 432. The distribution bus 432 is also connected, inthis embodiment, to other power sources generating three-phase 480VAC 60Hz power. One or more load circuits 435 are connected through circuitbreakers 434 to the distribution bus 432 and tap off power to feed tocustomer loads 436. In certain embodiments, one or more of lines 435carry three-phase power. In certain embodiments, one or more of lines435 carry single-phase power. In certain embodiments, the powerdistribution panel 430 is provided by a customer who is purchasing thepower being provided over line 419C.

The stator winding (not visible) of the WRSG 412 is coupled directly tothe distribution bus 432 and hence the rotational speed of the WRSG 412is fixed by the frequency of the distribution bus 432. The rotor winding(not visible) of the WRSG 412 is excited with direct current, forexample from the auxiliary load panel 416, using slip rings and brushes(not visible) or with a brushless exciter with a rotating rectifier (notvisible). The speed of the WRSG 412 is determined by the frequency ofthe rotating field created by the rotor and by the number of pole pairsof the rotor. For the example system of FIG. 14, the WRSG 412 includes a4-pole rotor and generates power at 60 Hz, and therefore operates at3600 RPM. In certain embodiments disclosed herein, the WRSG 412 replacesthe generator 24 of FIG. 2 and is driven by the turbine 66. The poweroutput of the WRSG 412 is determined by the torque input from theturbine 66, as the output voltage and frequency are fixed. In certainembodiments, a gearbox (not shown) is provided between the turbine 22and WRSG 412 as the turbine 22 preferentially operates at a much higherspeed, for example 52,000 RPM, compared to the speed of the WRSG 412,for example 3600 RPM.

FIG. 15 depicts a more detailed description of the control process 200of FIG. 10 with respect to the system 400 of FIG. 14 according tocertain aspects of this disclosure. In particular, the step 225 ofprocess 200 is expanded with respect to how this step is accomplishedwith a system 400 comprising a WRSG 412. The process 200 follows thesteps 205-220 as shown in FIG. 10, then transitions to step 452 of FIG.15 wherein the turbine speed is initially maintained using a fuelcontrol feedback loop such as shown in FIG. 16. In step 454, one or moreloads 424 are connected to the output of WRSG 412 by closing therespective relays 452 of load module 410 thereby stabilizing the speedof the WRSG 412. The amount of load provided by the load module 410 is afunction of the oxidizer 60 temperature, wherein very little load may berequired when the oxidizer 60 is cold while a large load may be requiredwhen the oxidizer 60 is hot. In certain embodiments, approximately 40 kWof load is added. In step 456, the speed of the WRSG 412 is then variedabout the nominal operating speed, for example the 3600 RPM disclosedabove, while the phase alignment between the three-phase output of theWRSG 412 and the existing three-phase voltage on distribution bus 432 ismonitored. When synchronization of the output of the WRSG 412 and theexisting voltage on distribution bus 432 is detected, relay 413 isclosed in step 458 thereby connecting the output of the WRSG 412 to thedistribution bus 432. As the speed is now controlled by the linefrequency on the distribution bus 432, the process moves to step 460 andcontrols the power output using a fuel control feedback loop such asshown in FIG. 17. The process then proceeds as shown in FIG. 10 startingat step 230.

FIG. 16 depicts an exemplary turbine speed control loop 500 adapted forthe process of FIG. 15 according to certain aspects of this disclosure.This control loop is operational during steps 452-456 of the process ofFIG. 15. The speed 186 of the WRSG 412 is sensed and fed back as asignal 186A to a summing junction 198 where the feedback signal 186A iscombined with a speed setpoint signal 184, producing a speed errorsignal 186B. A controller 510 accepts the error signal 186B and providesa control signal to a fuel controller 520 that adjusts the flow of fuel525 to the turbine 22 that drives the WRSG 412. With the fixed load ofthe load module 420, the speed of the WRSG 412 will vary in response tovariations in the fuel flow 525.

FIG. 17 depicts an exemplary power output control loop 550 adapted forthe process of FIG. 15 according to certain aspects of this disclosure.This control loop is operational during step 460 of the process of FIG.15. The output power 552 from the WRSG 412 is sensed and fed back assignal 556A to a summing junction 1558 where the feedback signal 556A iscombined with a speed setpoint signal 554, producing a speed errorsignal 556B. A controller 560 accepts the error signal 556B and providesa control signal to the fuel controller 520 that adjusts the flow offuel 525 to the turbine 22 that drives the WRSG 412. As the speed of theWRSG 412 is fixed in relation to the frequency and phase of the voltageon distribution bus 432, the power output of the WRSG 412 will vary inresponse to variations in the fuel flow 525 while the speed of the WRSG412 remains essentially constant.

FIG. 18 is an exemplary schematic of a power generation system 600according to certain aspects of this disclosure. The system 600 includesa turbine system 610 and can include the power distribution module 430from FIG. 14. The turbine system 610 includes, in this embodiment, apermanent magnet generator (PMG) 612 that provides three-phase power ata relatively high voltage, for example 600-800 VAC, at a relatively highfrequency, for example 2000-2400 Hz. In the embodiment of FIG. 18, thePMG provides an output of 600 VAC at 2 kHz. The power output 614 of thePMG 612 is coupled to a power converter 616 that converts the outputpower 614 to, in this example, three-phase 480VAC 60 Hz power on line622. In certain embodiments, the power converter 616 provides power atother frequencies and voltages. In certain embodiments, the powerconverter 616 provides single-phase and/or two-phase power. The turbinesystem 610 also includes, in this embodiment, a circuit breaker 620 onthe output of power converter 616.

In certain embodiments, the PMG 612 is coupled directly to the turbine22 (not shown in FIG. 18), eliminating the need for a gearbox. The rotor(not visible) of the PMG 612 includes a number of permanent magnetsarranged in a multi-pole configuration to provide the rotating magneticfield when the rotor is rotated by the turbine 22. The stator winding(not visible) of PMG 612 are connected to the power inverter 626. Incertain embodiments, the power converter 616 can accept a variable inputvoltage and frequency and provide the desired voltage and frequency online 622. This allows the turbine 22, and therefore the PMG 612, tooperate over a range of speed while still delivering power on line 622.

FIG. 19 depicts a more detailed description of the control process 200of FIG. 10 with respect to the system 600 of FIG. 18 according tocertain aspects of this disclosure. In particular, the step 225 ofprocess 200 is expanded with respect to how this step is accomplishedwith a system 600 comprising a PMG 612 and power converter 616. Theprocess 200 follows the steps 205-220 as shown in FIG. 10, thentransitions to step 652 of FIG. 19 wherein the turbine speed isinitially maintained using a fuel control feedback loop such as shown inFIG. 16. In step 654, a starting load is provided by the power converter616 thereby stabilizing the speed of the PMG 612. In certainembodiments, approximately 10 kW of load is added. In step 656, thespeed of the PMG 612 is controlled by varying the load provided by thepower converter 616. The process moves to step 658 which controls boththe amount of output power on line 622 and the speed of the PMG 612 bysimultaneously varying the fuel flow and load provided by the powerconverter 616 using a two-input, two-output control feedback system 700such as shown in FIG. 20. The process then proceeds as shown in FIG. 10starting at step 230.

FIG. 20 depicts an exemplary speed and temperature control loop 700adapted for the process of FIG. 19 according to certain aspects of thisdisclosure. This control loop is partially operational during step 656of the process of FIG. 19 and fully operational during step 658. In step656, the speed 722 of the PMG 612 is sensed and fed back as a signal556A to a summing junction 558 where the feedback signal 556A iscombined with a speed setpoint signal 554, producing a speed errorsignal 556B. A controller 710 accepts error signal 556B and provides acontrol signal 730 to the power converter 616 to vary the load providedby the power converter 616. The controller 710 also provides atemperature setpoint signal 724 that, in certain embodiments, is heldconstant during step 656. In certain embodiments, the gas temperature721 at the inlet of the turbine is fed back as signal 726A to a summingjunction 728 where it is combined with the temperature setpoint signal724 to generate a temperature error signal 726B that is fed to thetemperature controller 560. In certain embodiments, the controller 710provides a control signal 735 to the fuel controller 520 that overridesthe feedback error signal 726B and directly control the fuel flow 525while executing step 656. In certain embodiments, the temperaturecontroller 520 operates during step 656 to adjust the fuel flow 525 soas to maintain the gas temperature 721 at the setpoint 724. In certainembodiments, the controller 710 executes a pure integral controlfunction to generate control signal 735 so as to bring the PMG speed 722to the speed setpoint 724 while also achieving the starting load set instep 654.

In step 658, the controller 710 receives feedback signal 556A from thePMG speed 722, and adjusts both the temperature setpoint signal 724 andthe load control signal 730 to the power converter 616. In certainembodiments, a control algorithm within controller 710 that provides theload control signal 730 is faster than the control algorithm thatprovides the temperature setpoint signal 724, such that the speedcontrol provided by changes in the power converter 616 has a higherbandwidth than the speed control provided by changes in the fuel flow525. In certain embodiments, the controller 710 continues to provide theload control signal 730 as the process 200 continues to step 245 and theflow of the fuel gas 52 of FIG. 2 is varied by the temperaturecontroller 520 to maintain the turbine speed at S2 and the outlettemperature at T1. In certain embodiments, the functions of controller710 and temperature controller 520 are accomplished by a singlecontroller (not shown) that receives both the feedback signals 726A and556A and controls the fuel flow 525 directly as well as providing theload control signal 730.

FIG. 21 is a plot 800 of data illustrating an exemplary start-up processof a multi-combustor turbine system 50 according to certain aspects ofthis disclosure. The plot presents the values over time of the commandedflow rate 810 of fuel gas 52, with reference to the system of FIG. 2,and the power generation 820 as well as the operating variables ofwarmer 62 inlet temperature (WIT) 830, warmer 62 outlet/oxidizer 60inlet temperature (GIT) 840, oxidizer 60 exit/combustor 64 inlettemperature 850, combustor 64 outlet/turbine 66 inlet temperature 860,and turbine 66 outlet temperature 870.

The start-up process starts with the multi-combustor system 50 of FIG. 2being completely off and at ambient temperature. These results will bedescribed with reference to the system of FIG. 2 and the process flow200 of FIG. 10. The plot 800 starts at Time=0 (Time₀) when the turbinecombustor 64 is fired up to run on auxiliary fuel 54 in step 215. Theflow 810 of the fuel gas 50 is zero and power generation 820 is zero.The temperatures 830, 840, 850, 860, and 870 of the various componentsrise to steady levels and power generation 820 begins at a first powerlevel, for example at 50 kW. In certain embodiments, this is a load fromthe load module 420 of FIG. 14.

At Time₁, the warmer combustor 62 initially is operated using auxiliaryfuel 54 as disclosed in step 230. The temperatures 830, 840, 860, and870 of the various components again rise to higher steady levels andpower generation 820 rises to a second power level, for example 270 kW.The temperature 850 of the oxidizer 60 outlet does not reach a steadystate.

At Time₂, the flow 810 of fuel gas 50 of FIG. 2 is started as disclosedin step 235. The temperature 850 of the oxidizer 60 outlet continues torise, inflecting upwards from its previous trajectory upon theinitiation of the fuel gas flow 810. The power output 820 remainsrelatively constant as do the temperatures 830, 840, 860, and 870.

At Time₃, the temperature 850 of the oxidizer 60 outlet is nearing itstarget temperature and the auxiliary fuel 54 is turned off to theturbine combustor 64 as stated in step 240. As this directly affects thetemperature of the gas reaching the turbine 22, the temperatures 860 and870 of the gas at the turbine inlet and outlet, respectively, and thepower output 820 dip suddenly as the turbine combustor 64 goes out. Thetemperature 840 at the oxidizer 60 inlet starts to drop while the fuelflow 810 rises slowly. The temperature 850 of the oxidizer 60 outletcontinues to rise despite the drop in temperature 840, reflecting thelarge thermal mass and long time constant inherent in the design ofoxidizer 60.

At Time₄, still part of step 240, the flow of auxiliary fuel 54 is cutoff to the warmer 62 and the system 50 begins operation solely on fuelgas 50. The flow 810 of the fuel gas 50 continues to rise as the controlloop acts to bring the temperature 850 of the oxidizer outlet to atarget temperature, such as 1850° F. in the example of FIG. 21. Thepower output 820 also returns to its previous level as the temperature860 of the turbine 22 inlet rises again. The temperature 840 of theoxidizer 60 inlet drops again, reflecting the loss of heat from thewarmer 62. As the heat is now being provided in the oxidizer 60, thetemperature 850 of the oxidizer 60 outlet remains at the targettemperature despite the drop of over 300° F. in the temperature 840 ofthe oxidizer 60 inlet. This mode of operation is an example steady-stateoperating condition of the multi-combustor turbine system 50 disclosedherein. In certain embodiments that include a WRSG 412 of FIG. 14, thissteady-state operation is maintained by the control loop of FIG. 17. Incertain embodiments that include a PMG 612 of FIG. 18, this steady-stateoperation is maintained by the control loop of FIG. 20.

The concepts disclosed herein provide a system and method of graduallyoxidizing at least a portion of a fluid that includes an oxidizablefuel. This system uses a turbine to drive a compressor that compressesthe fluid that comprises the fuel that is then heated in an oxidizerwherein the heated compressed fluid is then used to drive the turbine.In certain embodiments, this system also includes a power generator. Thesystem is adapted to provide a self-sustaining oxidation process withinan oxidizer having an incoming fluid flow that comprises a fuel contentof less than about 5% fuel (e.g. methane) that will not support a stablecombustion flame. The disclosed systems include one or both of a turbinecombustor and a warmer combustor used during the start-up process tobring the oxidizer up to the self-ignition temperature of the fuel. Oncethe oxidizer reaches a temperature that is at or near the self-ignitiontemperature of the fuel, one or both of the turbine combustor and thewarmer combustor may be shut off. The system regulates the amount offuel introduced into the fluid flow so as to control the temperature ofthe gas exiting the oxidizer and the load placed on the turbine by apower generator so as to control the turbine speed.

The previous description is provided to enable a person of ordinaryskill in the art to practice the various aspects described herein. Whilethe foregoing has described what are considered to be the best modeand/or other examples, it is understood that various modifications tothese aspects will be readily apparent to those skilled in the art, andthe generic principles defined herein may be applied to other aspects.Thus, the claims are not intended to be limited to the aspects shownherein, but is to be accorded the full scope consistent with thelanguage claims, wherein reference to an element in the singular is notintended to mean “one and only one” unless specifically so stated, butrather “one or more.” Unless specifically stated otherwise, the terms “aset” and “some” refer to one or more. Headings and subheadings, if any,are used for convenience only and do not limit the disclosure.

It is understood that the specific order or hierarchy of steps in theprocesses disclosed is an illustration of exemplary approaches. Basedupon design preferences, it is understood that the specific order orhierarchy of steps in the processes may be rearranged. Some of the stepsmay be performed simultaneously. The accompanying method claims presentelements of the various steps in a sample order, and are not meant to belimited to the specific order or hierarchy presented.

Terms such as “top,” “bottom,” “front,” “rear” and the like as used inthis disclosure should be understood as referring to an arbitrary frameof reference, rather than to the ordinary gravitational frame ofreference. Thus, a top surface, a bottom surface, a front surface, and arear surface may extend upwardly, downwardly, diagonally, orhorizontally in a gravitational frame of reference.

A phrase such as an “aspect” does not imply that such aspect isessential to the subject technology or that such aspect applies to allconfigurations of the subject technology. A disclosure relating to anaspect may apply to all configurations, or one or more configurations. Aphrase such as an aspect may refer to one or more aspects and viceversa. A phrase such as an “embodiment” does not imply that suchembodiment is essential to the subject technology or that suchembodiment applies to all configurations of the subject technology. Adisclosure relating to an embodiment may apply to all embodiments, orone or more embodiments. A phrase such an embodiment may refer to one ormore embodiments and vice versa.

The word “exemplary” is used herein to mean “serving as an example orillustration.” Any aspect or design described herein as “exemplary” isnot necessarily to be construed as preferred or advantageous over otheraspects or designs.

All structural and functional equivalents to the elements of the variousaspects described throughout this disclosure that are known or latercome to be known to those of ordinary skill in the art are expresslyincorporated herein by reference and are intended to be encompassed bythe claims. Moreover, nothing disclosed herein is intended to bededicated to the public regardless of whether such disclosure isexplicitly recited in the claims. No claim element is to be construedunder the provisions of 35 U.S.C. §112, sixth paragraph, unless theelement is expressly recited using the phrase “means for” or, in thecase of a method claim, the element is recited using the phrase “stepfor.” Furthermore, to the extent that the term “include,” “have,” or thelike is used in the description or the claims, such term is intended tobe inclusive in a manner similar to the term “comprise” as “comprise” isinterpreted when employed as a transitional word in a claim.

What is claimed is:
 1. A system for gradually oxidizing fuel,comprising: an oxidizer having a reaction chamber with an inlet and anoutlet, the reaction chamber configured to receive a gas comprising anoxidizable fuel through the inlet, the oxidizer configured to maintain aflameless oxidation process; a first heating chamber with an inlet andan outlet, the inlet of the first heating chamber in fluid communicationwith the outlet of the reaction chamber, the first heating chamberconfigured to receive the gas from the reaction chamber and to heat thegas; a turbine having an inlet and an outlet, the inlet of the turbinecoupled to the outlet of the first heating chamber and configured toreceive the gas from the first heating chamber; a compressor coupled tothe inlet of the reaction chamber to compress the gas prior to the gasbeing received by the reaction chamber; a second heating chamber coupledbetween the compressor and the inlet of the reaction chamber, the secondheating chamber being configured to receive the compressed gas from thecompressor and to heat the gas prior to the gas being received by thereaction chamber; and a heat exchanger having a first portion coupledbetween the compressor and the second heating chamber such that the gasfrom the compressor passes through the first portion before the gas isreceived by the second heating chamber, and a second portion coupled tothe outlet of the turbine such that the gas from the turbine passesthrough the second portion, the heat exchanger configured to thermallycouple the gas in the second portion to the gas in the first portion. 2.The system of claim 1, wherein the oxidizer further comprises a porousmedia disposed within the reaction chamber.
 3. The system of claim 1,wherein the oxidizer further comprises at least one anchor heater thatis at least partially disposed within the reaction chamber.
 4. Thesystem of claim 1, wherein the oxidizer does not comprise a catalyst forthe oxidation process.
 5. The system of claim 1, wherein the oxidizer isfurther configured to maintain the oxidation process when the fuelcontent of the gas is below a level that will sustain a continuousflame.
 6. The system of claim 5, wherein the oxidizer is furtherconfigured to maintain the oxidation process when the gas comprises lessthan 5% oxidizable fuel.
 7. The system of claim 6, wherein the oxidizeris further configured to maintain the oxidation process when theoxidizable fuel is methane.
 8. The system of claim 1, wherein the firstheating chamber comprises a burner configured to ignite a combustiblefuel-air mixture.
 9. The system of claim 1, wherein the second heatingchamber comprises a burner configured to ignite a combustible fuel-airmixture.
 10. The system of claim 1, further comprising a power generatorcoupled to the turbine, the power generator configured to be driven bythe turbine.
 11. The system of claim 1, wherein: the gas comprises atleast one volatile organic compound (VOC); and the oxidizer achieves atleast partial oxidation of the VOC.
 12. A gradual oxidation systemcomprising: a compressor configured to receive and compress a gascomprising a fuel-air mixture; a warmer coupled to the compressor, thewarmer configured to receive the gas from the compressor and to heat thegas; a reaction chamber coupled to the warmer, the reaction chamberconfigured to receive the gas from the warmer and maintain a flamelessoxidation process of the fuel-air mixture without a catalyst; a heatercoupled to the reaction chamber, the heater configured to receive thegas from the reaction chamber and heat the gas; a turbine coupled to theheater and the compressor, the turbine being configured to receive thegas from the heater and expand the gas; and a controller coupled to thewarmer and the heater, the controller configured to control the heatingof the gas in the warmer and in the heater, wherein the controller iscoupled to a sensor that measures a temperature of the gas at the outletof the reaction chamber, the controller further configured to direct thewarmer to heat the gas until the temperature reaches a setpoint.
 13. Thesystem of claim 12, further comprising a power generator coupled to theturbine and the controller, wherein the turbine is configured to drivethe power generator and the controller is configured to control thepower generator to maintain the turbine speed within a determined range.14. A system for gradually oxidizing fuel, comprising: an oxidizerhaving a reaction chamber with an inlet and an outlet, the reactionchamber configured to receive a gas comprising an oxidizable fuelthrough the inlet of the reaction chamber, the oxidizer configured tomaintain a flameless oxidation process, wherein the oxidizer furthercomprises at least one anchor heater that is at least partially disposedwithin the reaction chamber; and a heating chamber with an inlet and anoutlet, the inlet of the heating chamber in fluid communication with theoutlet of the reaction chamber, the heating chamber configured toreceive the gas from the reaction chamber and to heat the gas.
 15. Thesystem of claim 14, wherein the heating chamber comprises a burnerconfigured to ignite a combustible fuel-air mixture.
 16. The system ofclaim 14, wherein the oxidizer further comprises a porous media disposedwithin the reaction chamber.
 17. The system of claim 14, wherein theoxidizer does not comprise a catalyst for the oxidation process.
 18. Thesystem of claim 14, wherein the oxidizer is further configured tomaintain the oxidation process when the fuel content of the gas is belowa level that will sustain a continuous flame.
 19. The system of claim14, wherein: the gas comprises at least one volatile organic compound(VOC); and the oxidizer achieves at least partial oxidation of the VOC.20. A system for gradually oxidizing fuel, comprising: a heating chamberwith an inlet and an outlet, the heating chamber configured to receiveand heat a gas comprising an oxidizable fuel; and an oxidizer having areaction chamber with an inlet and an outlet, the inlet of the reactionchamber in fluid communication with the outlet of the heating chamber,the reaction chamber configured to receive the gas from the heatingchamber, the oxidizer configured to maintain a flameless oxidationprocess, wherein the oxidizer further comprises at least one anchorheater that is at least partially disposed within the reaction chamber.21. The system of claim 20, wherein the heating chamber comprises aburner configured to ignite a combustible fuel-air mixture.
 22. Thesystem of claim 20, wherein the oxidizer further comprises a porousmedia disposed within the reaction chamber.
 23. The system of claim 20,wherein the oxidizer does not comprise a catalyst for the oxidationprocess.
 24. The system of claim 20, wherein the oxidizer is furtherconfigured to maintain the oxidation process when the fuel content ofthe gas is below a level that will sustain a continuous flame.
 25. Thesystem of claim 20, wherein: the gas comprises at least one volatileorganic compound (VOC); and the oxidizer achieves at least partialoxidation of the VOC.
 26. A gradual oxidation system comprising: acompressor configured to receive and compress a gas comprising afuel-air mixture; a warmer coupled to the compressor, the warmerconfigured to receive the gas from the compressor and to heat the gas; areaction chamber coupled to the warmer, the reaction chamber configuredto receive the gas from the warmer and maintain a flameless oxidationprocess of the fuel-air mixture without a catalyst; a heater coupled tothe reaction chamber, the heater configured to receive the gas from thereaction chamber and heat the gas; a turbine coupled to the heater andthe compressor, the turbine being configured to receive the gas from theheater and expand the gas; and a controller coupled to the warmer andthe heater, the controller configured to control the heating of the gasin the warmer and in the heater, wherein the controller is coupled to asensor that measures a temperature of the gas at the inlet of theturbine, the controller further configured to direct the heater to heatthe gas until the temperature reaches a setpoint.
 27. The system ofclaim 26, further comprising a power generator coupled to the turbineand the controller, wherein the turbine is configured to drive the powergenerator and the controller is configured to control the powergenerator to maintain the turbine speed within a determined range.